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Cancer Rates Higher in Both Type 1 and Type 2 Diabetes

High glucose, obesity studied for possible link to cancer development…

The findings highlight the importance of screening for carcinomas in patients with diabetes to aid early detection and reduce premature mortality, say the researchers.

The Australian researchers found that the highest excess risks were observed for cancers of the pancreas, liver, endometrium, kidney, thyroid, and gallbladder and for chronic myeloid leukemia.

The researchers note that the heightened medical attention given directly after a diabetes diagnosis, as well as reverse causality, might partly explain the increased cancer risk seen initially, but these factors “do not explain increased risks 2 years following diabetes diagnosis, particularly for cancers of the pancreas, liver, kidney, and endometrium.”

The study included 953,382 registrants from the National Diabetes Service Scheme (NDSS) in Australia: 80,676 (8.5%) with type 1 diabetes and 872,706 (91.5%) with type 2 diabetes, diagnosed between the years 1997 and 2008. The NDSS is one of the world’s largest diabetes registries, and the data were linked to the National Death Index (NDI).

This information was then linked to data from the Australian Cancer Database (ACD) to calculate standardized incidence and mortality rates of cancer overall and site-specific cancers in patients with diabetes. Cancer rates in Australia’s general population served as a comparison.

Individuals were followed from January 1, 1997 (or registration date if later) to December 31, 2008, date of death, or date of event (death or cancer occurrence).

This study is one of the first to explore site-specific cancer mortality in type 1 diabetes, the researchers note.

Standardized incidence ratios in patients with type 1 diabetes for all cancers combined were 1.02 for males and 1.10 for females.

Among females with type 1 diabetes, there were significant excess risks for cancers of the pancreas, liver, esophagus, colon and rectum, stomach, thyroid, brain, and lung, as well as ovarian and endometrium cancer, and a decreased risk for melanoma, compared with the general population. For men, a similar pattern was seen, but fewer associations were significant. A decreased incidence of prostate cancer was found.

Significant increased mortality ratios were seen for cancers of the pancreas and liver and non-Hodgkin’s lymphoma among those with type 1 diabetes and for cancers of the kidney (in males only) and, in women, for brain and endometrial cancers.

For type 2 diabetes, the standardized incidence ratios for cancers overall were 1.08 for males and 1.22 for females. Significant elevated incidence ratios were seen for all cancers in type 2 diabetes, excluding brain, anal (in females), testicular cancers (in men), and esophageal cancer (in females).

Melanoma and prostate cancers showed significant decreased risk, while the highest excess risks were observed for cancers of the liver and pancreas.

For type 2 diabetes, significantly increased death rates were found for cancers of the pancreas, liver, and kidney and Hodgkin’s lymphoma. In females only, significant increased mortality was also found for stomach and gallbladder cancer and non-Hodgkin’s lymphoma.

Studies based on cohorts with detailed information on type 2 diabetes that were able to account for obesity, lifestyle-related factors, and diabetes treatment have still observed elevated risks for a number of cancers, they point out. “Therefore, it is unlikely that these factors explain the entire association between diabetes and cancer.”

As a similar level of excess risk for cancer was found for both types of diabetes (although fewer outcomes were significant for type 1 diabetes, most likely due to limited power) it is unlikely that insulin is the driving force, the researchers say. Instead, they suggest that hyperglycemia may be a contributing factor.

Practice Pearls:

  • The findings highlight the importance of screening for carcinomas in patients with diabetes to aid early detection and reduce premature mortality.
  • Cancers diagnosed many years after diabetes diagnosis are more likely to have occurred as a consequence of diabetes.
  • It is unlikely that insulin is the driving force, the researchers say. Instead, they suggest that hyperglycemia may be a contributing factor.

Diabetes Care. Published online December 8, 2014. Abstract.